By Ives Galarcep

A quartet of tightly-contested conference semifinal first legs means all four MLS playoff series are still up for grabs. Here's what to expect from all four decisive second legs.

Call it a clash of generations. In one corner, you have four of the most respected coaches in Major League Soccer, veteran leaders with some of the best resumes in league history. In the other corner you have four of the youngest coaches and brightest minds in the league. The two sides aren’t exactly operating as teams, but how both sides do just might offer us a glimpse of what to expect in the league in years ahead.

On one corner you have the ‘Brat Pack’, a foursome all aged 40 or younger, each of which turned in truly impressive 2013 performances. Mike Petke and Caleb Porter took the league by storm in their first years as pro head coaches, leading their respective conferences and helping both teams build championships aspirations that feel far more realistic than anyone could have imagined.

Jay Heaps’ second season in charge of New England went better than most would have imagined, as he helped transform the Revs from an afterthought to a young team with a dangerous attack and significantly improved defense.

Then you have Jason Kreis, who is the oldest of the younger generation, and who can hardly be called new at the craft, having just completed his seventh season in charge of Real Salt Lake. Already one of the most respected coaches in the league, Kreis has just coached one of his best seasons to date, taking a team in transition and leading it through another quality season.

All four young coaches are facing older, more seasoned adversaries who will look to use their experience to make the difference in the nail-biting second legs that lie ahead. Bruce Arena, Dominic Kinnear, Sigi Schmid and Peter Vermes have combined for six MLS Cup titles and six U.S. Open Cups between them, but all four coaches could be eliminated from the playoffs by the end of the week.

That precarious positions exist after four first legs that didn’t all go as expected. The LA Galaxy’s narrow win against Real Salt Lake wasn’t much of a surprise, but New England’s impressive victory against Sporting KC was. Portland grabbed a first leg win on the road in Seattle to take control of the Cascadia series, while the New York Red Bulls squandered a golden opportunity to put their series against Houston out of reach by blowing a 2-0 lead in an eventual 2-2 draw that saw Jamison Olave sent off.

Just which teams survive this week’s decisive second legs will come down to which coaches put together the best game plans, and make the right lineup decisions. The smart money will be on the older coaches having an edge, but if you the younger generation has shown anything, it is that they are more than capable of matching wits with the elder statesmen.

Here is a closer look at all four conference semifinal second legs, and what it will take for each team to come away victorious:

HOUSTON at NEW YORK

What the Red Bulls need to do to win: Avoid mistakes in defending the wings, which means David Carney playing much better than he did in the first leg. Getting the ball to Thierry Henry, who will need to float deeper to stretch the Dynamo defense, and create space for players like Cahill and Peguy Luyindula to run into.

What the Dynamo need to do to win: Look to use its speed to go after Carney and Markus Holgersson, with Oscar Boniek Garcia and Omar Cummings having the pace to wreak havoc. Will Bruin will need to make his presence felt as well, and should benefit the most from Olave’s absence. That alone won’t win it for Houston though. The Dynamo need the midfield to win a tough battle against the likes of Cahill and Dax McCarty.

The pick: Red Bulls defense holds firm despite Jamison Olave’s absence, and Thierry Henry proves to be too much to handle as the home team posts a 2-1 victory, advancing 4-3 on aggregate.

NEW ENGLAND at SPORTING KC

What Sporting KC needs to do to win: Peter Vermes’ decision to start Teal Bunbury in the first leg didn’t go so well, so look for him to switch things up and go back to Dom Dwyer or Claudio Bieler. Aurelien Collin needs to be smarter about challenges and watch his positioning. Assuming Vermes doesn't bench him in favor of Ike Opara. Sporting definitely needs more production from the flanks, which will be key to completing the comeback.

What the Revolution needs to do to win: The Revs finally showed an ability to break down Sporting KC’s defense, and it took some sharp passing and combination play to do it. The looks won’t be as easy to come by on the road, but getting Kelyn Rowe on the ball, and Juan Agudelo winning the physical battle in the penalty area is a start. Containing Graham Zusi is also a must, which will be easier said than done for a team without a true defensive midfielder.`

The pick: Zusi has a stellar outing, and Dwyer emerges to be the goalscorer KC needed. Sporting’s defense holds in a 2-0 victory, sending Sporting KC through, 3-2, on aggregate.

SEATTLE at PORTLAND

What the Timbers need to do to win: The Timbers could play the same way they played in the first leg in Seattle and probably get the result they need, but Caleb Porter isn’t about to defend and counter at Jeld-Wen Field. Look for the Timbers to attack from the start, and look for a match-settling early goal to really put the pressure on Seattle. If Max Urruti is healthy enough to start, he could give the Timbers the tricky forward they need to really unsettle’s Seattle’s defense (not that first-leg goal-scorer Ryan Johnson would be a bad option to start again at this point).

What the Sounders need to do to win: Lamar Neagle’s energy will be missed, but if Obafemi Martins is healthy enough to play he should give the Sounders more of a threat in the final third. Seattle needs to do a better job of building through the middle, rather than settling for service from the wings, which Portland’s big centerbacks dealt with far too easily. Mauro Rosales needs to create and pick apart the Timbers’ tough central midfield, otherwise Seattle will very likely have to settle for long-range shots that do little to trouble Donovan Ricketts.

The pick: The Timbers score an early goal to take control, and never let up, coasting to an impressive second leg win. Timbers advance, 4-1 on aggregate.

LA GALAXY at REAL SALT LAKE

What the Galaxy needs to do to win: LA has to know RSL will look to press the action early, which should create some good opportunities to counter. Keane and Landon Donovan have to finish chances when they come, and Gyasi Zardes has to make sure to track back and help the LA defense.

What Real Salt Lake need to do to win: The midfield was far too sloppy in the first leg, so cleaning up the erratic passing is step one to having a better match. Kreis needs either Joao Plata or Robbie Findley in the starting lineup to give the Galaxy defense some speed to worry about, and RSL needs to get Javier Morales more involved. Without him orchestrating the attack at its best, the home team won’t be able to match firepower with the Galaxy. RSL needS to get rookie Kofi Opare in space, and really test him in a way it simply didn’t in the first leg.

The pick: RSL should be able to put some pressure on LA early on, but if the early goal doesn’t come, the Galaxy could settle in and start picking apart the RSL transition defense on counterattacking breaks. Look for Robbie Keane to take his chances in a way he didn’t in the first leg, and the Galaxy’s counterattacking is just too much for RSL to handle. The Galaxy post a 2-1 road win, and take the series, 3-1 on aggregate.